LAKE FOREST, Calif. — When John McCain and Barack Obama appear on the same stage today, they will vividly demonstrate the reach that has made the Rev. Rick Warren among the most significant evangelists of his generation.

He’s a megastar who leads the nation’s fourth-largest church and reaches thousands of ministers through the Internet and crusades against poverty and AIDS. That globe-trotting work and his successful book — “The Purpose-Driven Life: What on Earth Am I Here For?” — puts him at the vanguard of a movement that inspires young, socially conscious Christians.

But his willingness to soft-pedal political issues once central to U.S. evangelicals, such as opposition to abortion, has opened him to criticism that he has strayed from his calling to spread the Gospel.

Today’s forum also is a sign of religion’s importance in the 2008 presidential campaign, and the emergence of a new style of evangelical leadership on the national stage that is not tied to a single party and has broadened its social agenda beyond that of the religious right.

“This is absolutely a changing of the guard, and it suggests that the new guard of the evangelical movement is able to generate the attention and focus of both parties,” said D. Michael Lindsay, a sociologist at Rice University and author of “Faith in the Halls of Power: How Evangelicals Joined the American Elite.”

Warren personally invited the two candidates — “friends of mine” — via their cellphones. His event at the Saddleback Church will be broadcast live on CNN and Fox News Channel and streamed on the Web. It has among its aims “helping the church regain credibility and encouraging our society to return to civility,” he said.

It’s likely that fans and critics will be watching closely when Warren, 54, hosts the presidential contenders at the church complex in Lake Forest, home to 22,000 weekend worshippers.

The presumptive Democratic and Republican nominees won’t debate during the Civil Forum on the Presidency. But they will make a brief joint appearance, their first of the campaign, and Warren will interview each separately about the Constitution, poverty, AIDS, human rights and other subjects.

“America has a choice. It’s not between a stud and a dud this year,” Warren said. “Both of these men care about America. My job is to let them share their views.”

New breed of evangelicals

The event will play to one of Obama’s strengths, talking about his Christian faith, but it also will underscore the gulf between his views and those of the most conservative Christian voters. The forum also gives him a perfect setting to counter the misperception that he is Muslim. A recent poll by the Pew Research Center for the People and the Press found that 12 percent of respondents believe the Illinois senator is Muslim.

The benefit of the forum to McCain, who attends a Baptist church, is less clear. While many of his views, including opposition to abortion, match the outlook of conservative Christians, the Arizona senator is far less comfortable than Obama discussing his faith.

McCain did not participate in a spring forum at Messiah College near Harrisburg, Pa., where Obama and New York Sen. Hillary Rodham Clinton discussed religion and their personal lives.

Larry Ross, who represents Warren, said the pastor has been consulting other clergy and with experts in different fields to develop questions for the candidates.

Many evangelicals think Warren’s growing profile and his willingness to welcome Obama to his pulpit are evidence that he has emerged as the most pivotal figure in U.S. evangelicalism.

The pastor, they said, is emblematic of a new breed of evangelicals who put social justice ahead of partisan politics. Some go so far as to call the plain-talking Warren, a man who prefers blue jeans and Hawaiian shirts to business suits, the Billy Graham of his era.

“He’s a guy whose message has met the right moment,” said Richard Land, a leading authority with the Southern Baptist Convention, the denomination to which Warren’s church belongs.

Detractors see Warren as a spiritual entrepreneur who has built his empire on what they call generic self-help ideas found in “The Purpose-Driven Life.”

“For many evangelical leaders, Rick Warren is either a little too naive or a little too shrewd,” said the Rev. Rob Schenck, president of the National Clergy Council, a Washington group that works to meld Christian teachings into the debate over public policies.

“He is threatening to water down the essential message of evangelical Christianity,” Schenck said.

“Just a regular guy”

Warren insists he remains firmly tied to his Southern Baptist roots.

He opposes abortion and defines marriage as the union of a man and a woman. He has hosted politically conservative figures, such as Sen. Sam Brownback, R-Kan.

But Warren said he also is inspired by the broader message of faith and compassion in the Bible.

The forum with McCain and Obama, he said, is his latest attempt to introduce civility into public discourse, even if it irks some fellow evangelicals.

“Jesus told us to love our neighbor, even if they don’t agree with you,” Warren said.

“The Purpose-Driven Life,” published in 2002, helped create this reach. “It’s not about you,” Warren writes in the opening of the book, which has sold 35 million copies in 50 languages.

The senior managing editor of ChristianityToday, Mark Galli, said Warren “has that gift of being able to popularize ideas that are in some ways commonplace.” Galli’s magazine in 2002 described Warren as “just a regular guy who may be America’s most influential pastor.”

Warren wants to mobilize 1 billion Christians to attack what he calls “five global giants”: spiritual emptiness, corrupt leadership, poverty, disease and illiteracy. His church has sent more than 7,000 volunteers to dozens of developing and Third World countries. Rwandan President Paul Kagame has spoken of his country becoming “the first purpose-driven nation.”

Following the lead of his wife, Kay, Warren also has championed the fight against AIDS in Africa, rallying support for U.S. relief programs.

Warren shrugs off criticism, insisting he is doing God’s work, if on a scale most churches can only imagine. “As a pastor, if you love people, they will follow you,” he said. “I believe that Jesus Christ changes lives.”

Material from The Christian Science Monitor and The Associated Press is included.